Since the emergence of nanostructures as technologically relevant materials, “bottom-up” fabrication strategies and directed assembly methods have become increasingly attractive. Due to their potential for proliferating a new generation of electronic devices, the need for the development of nanostructures has been noted in the International Technology Roadmap for Semiconductors.
In the current state-of-the-art “bottom-up” assembly of nanodevices, that is, devices containing nano-scale components such as nanowires, multi-step preparatory routines involving the formation, transfer, and alignment of nanowires are typically practiced. Specifically, in such routines nanowires are grown on a primary substrate, then removed from the substrate and transferred to a solution. The nanowires are then transferred from the solution to a secondary substrate, where an alignment technique is employed to align the nanowires with one another. Several techniques for aligning nanowires and controlling nanowire hierarchy have been developed. These techniques include electric field assisted orientation and alignment with fluid flow in microchannels. More recent advances have involved the confinement and alignment of nanowires using the Langmuir-Blodgett technique, assembly of densely packed elongated metal nanowires using a pattern transfer process, microcontact printing, and large-area blown bubble films of aligned nanowires.
These multi-step growth and alignment techniques are lacking in their capability to accurately and repeatedly position nanowires at predetermined coordinates on a substrate. The capability of accurately and repeatedly positioning nanowires at selected coordinates is critical for nanofabrication at technologically relevant scales, in particular for facilitating the subsequent processing steps which involve integration of nanowires with micro-scale and nano-scale components.